To control costs, firms including Citigroup Inc. and Time Warner are selling their jets. Alcatel-Lucent has allowed leases on two jets to expire and has put its third jet up for sale.

Jet brokers say the market has constricted in recent months. “Our inventory is up dramatically, and demand is way down," said Josh Messinger, of J. Messinger Corporate Jet Sales Inc., a jet broker.

For business jets, carrying costs are high—a Gulfstream 550 costs about $47 million. The corporate side of the business is particularly vulnerable. “They are not going to do employee layoffs and keep the jets," said Mary Hevener, a tax adviser at Morgan Lewis and Bockius.